Proton Ionic Liquid Modulates Hydrogen Coverage and Subsurface Absorbed Hydrogen to Enhance Pd Metallene Electrocatalytic Semi‐hydrogenation of Alkynols

Abstract

Electrochemical semi‐hydrogenation of alkynols to produce high‐value alkenols is a green and sustainable approach. Although Pd can exhibit excellent semi‐hydrogenation properties, its intrinsic mechanism still lacks in‐depth study. Herein, a proton ionic liquid (PIL)‐modified Pd metallene (Pdene@PIL) is synthesized for the electrocatalytic semi‐hydrogenation of 2‐methyl‐3‐butyn‐2‐ol (MBY) to 2‐methyl‐3‐buten‐2‐ol (MBE). The PIL modification of Pdene@PIL resulted in an MBY conversion of 96.1% and MBE selectivity of 97.2%, respectively. Theoretical calculations indicate the electron transfer between Pdene and PIL, leading to easier adsorption of MBY on the Pd surface. The d‐band center of Pdene@PIL shifts away from the Fermi level, which weakens the adsorption of over‐hydrogenated intermediates. At the same time, the PIL modification facilitates the adsorption of surface‐adsorbed hydrogen (H*ads) and inhibits the formation of subsurface‐absorbed hydrogen (H*abs). In particular, the PIL modification optimizes Hads* coverage, reduces the reaction energy of the rate‐determining step (C5H8O*‐C5H9O*), and inhibits HER. The reduction of H*abs formation inhibits the transfer of Pd to PdHx and suppresses the over‐hydrogenation. This work provides new insights into the modulation of H* to enhance the alkynol electrocatalytic semi‐hydrogenation reaction (ESHR) process from the perspective of surface modification.